Getting JSON parent node with Java JsonPath

Question

I'm having some trouble trying query a JSON with Java JsonPath.

I have a large json with informations about people location (thousand of lines). The field to find the person location is your macAdreess. The macAdreess does not repeat, in other words when I query for a specific macAdreess, I got once result.

This is a small piece of my Json:

{
   "readings": [
      {
         "value": {
            "floorRefId": "-4564288095083560912",
            "x": 86.405304,
            "y": 64.4601,
            "z": 0
         },
         "tags": {
            "macAddress": "f8:e0:79:82:95:92"
         },
         "timestamp": 1494620148598
      },
      {
         "value": {
            "floorRefId": "-4564288095083560912",
            "x": 86.540474,
            "y": 64.12458,
            "z": 0
         },
         "tags": {
            "macAddress": "f4:f5:24:96:d5:cd"
         },
         "timestamp": 1494620148598
      },
      {
         "value": {
            "floorRefId": "-4564288095083560912",
            "x": 86.31584,
            "y": 64.410446,
            "z": 0
         },
         "tags": {
            "macAddress": "f4:f5:24:2a:9c:13"
         },
         "timestamp": 1494620148598
      },
   ],
   "gateway_uuid": "cccccccc-9f70-4d93-94be-2fa7e15ef292",
   "status": "running"
}

I will need to query for one macAddress into JSON every five seconds, so if I need to traverse all JSON content, I will have a performance trouble.

Then I'm trying to use Java JsonPath API to query the macAdreess and it's running ok. But I need to get the parent node to get the location fields.

With this code:

public static void main(String[] args) throws Exception {
    String json = getJsonAsString();
    List<Map<String, Object>> expensive = JsonPath.parse(json).read("$..[?(@.macAddress=='f4:f5:24:96:d5:cd')]");
    System.out.println(expensive);
}

I got thit result:

[{"macAddress":"f4:f5:24:96:d5:cd"}]

You say that you will have performance trouble if you traverse the JSON your self. What do you think JsonPath is doing if not traversing the JSON? — bhspencer
– bhspencer, Commented May 13, 2017 at 22:20
It works! About performance trouble you are right! Maybe traversing the JSON by myself I will get more performance! Thanks a lot! — Luciano Nunes
– Luciano Nunes, Commented May 13, 2017 at 22:51

OneCricketeer · Accepted Answer · 2017-05-13 22:33:28Z

1

You need to query from the parent, and don't use the $.. deep scan.

$.readings[?(@.tags.macAddress=="f4:f5:24:96:d5:cd")]

But if you know there's only one, you'd be better off to linearly scan the data yourself. It would be more performant

answered May 13, 2017 at 22:33

OneCricketeer

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